Calcining and ore reduction oven



April 9, 1963 J. A. FAGNANT CALCINING AND ORE REDUCTION OVEN Filed June 27, 1961 A'ITORNEYS Ute This invention relates broadly to improvements in ovens designed for performing roasting Operations such, for example, as the calcning of limestone or similar materials, reducing metallic oxide ores and beneficiation of phosphate ore.

Many Western phosphate ores have relatively large amounts of carbonaceous material which lower the 1 content and interfere with electric furnace operation for the recovery of the phosphorus pentoxide.

An object of the present invention is to provide a novel oven structure wherein phosphate ores of this type may be satisfactorily employed for burning off all of the carbonaceous materials from the phosphate or so that the percentage of the P O in the product may be raised and the product made suitable for feeding into the electric furnace.

Another object of the present invention is to provide a new and novel oven structure which is particularly efficient for calcining limestone or similar materials by the provision of an inclined floor roasting chamber over lying an air plenum chamber through which air may be supplied for combustion of fuel in the roasting chamber while the material under treatment moves in a controlled depth layer, by -gravity to a discharge outlet.

Another object of the invention is -to provide an oven structure wherein a roasting chamber is provided with an inclined floor of castable refractory, which is slotted and rests upon supporting piers in a plenum chamber into which air is introduced for passage through the slots of the floor. The invention broadly contemplates the provision of an elongate inclined oven structure having a bottom wall provided with upstanding piers upon which is supported a slotted floor of high quality castable refractory. The floor forms the top of and closes a plenum chamber from which the prescri bed air escapes only through the floor into the overlying roasting chamber. Means is provided in the Construction of the top wall or roof of the roasting chamber for concentrating heat at the inlet for the chamber through which the material to be treated is introduced and which inlet or material admission throat also meters the flow of material to maintain the latter in a bed of desired depth. At the lower end of the slotted floor a discharge slot is provided which extends across the width of the chamber and which leads downwardly through a dischar-ge area to a unit which may be employed merely to guide the material onto a conveyor or to additionally subject the material to a cooling action as it passes from the oven .to the conveyor. Means is provided at the lower end of the chamber and immediately above the outlet slot for the roasting chamber for carrying off products of combustion and where the oven is employed for the roasting or calcining of limestone, such carry ofi means may be employed for recovery of 00 The inventiou will be best understood from a consideration of the following -detailed description taken in connection with the accompanying drawings forming a part of this specification with the Understanding, however, that the invention is not confined to a strict conformity with the showing of the drawings but may be changed or modified so long as such changes or modifications mark no material departure from the salient features of the invention as deiined by the appended claims.

In the drawings:

FIG. 1 shows a vertical longitudinal section through an oven structure constructed in accordance with the present invention.

FIG. 2 is a sectional view taken substantially on the line 2-2 of FIG. 1 looking in the direction of the arrows.

FIG. 3 is a partial section taken substantially on the line 3-3 of FIG. l looking in .the direction of the arrows.

Referring nowt more particularly to the drawings the numeral 10 generally designates the 'oven of the present invention which is preferably of elongate design as shown in FIG. 2 and includes the top wall 12, the bottom wall 14, the side walls 16 and the lower forward and upper rearward end walls 18 and 20 respectively.

The forward wall 18 is of substantial length transversely of the oven structure as shown in FIG. 2 and as shown in this View the side walls conver-ge slightly toward the rearward wall 20.

'Ihe entire oven structure is supported upon a suitable -foundation 22, to dispose the same, particularly the bottom wall 14, at an inclination from the horizontal with the forward wall 18 being at the lowest elevation.

The forward wall 18 is of materially greater height than the rearward wall 20 and leading therefrom at the top 'or upper part thereof and approximately on the lon- -gitudinal center of the furnace structure is the. outlet conduit 24 for carrying off products of combustion and this conduit at its outer end communicates with the vertical stack 26.

The top wall 12, which forms the roof of the roasting chamber C is preferably disposed at approximately the same inclination as the bottom wall 14 and .the upper end of the top wall 12 joins a downwardly and rearwardly extending short portion 12a which in turn joins a shorter rearwardly cxtending portion 12b, the inner or under side of which is disposed in close proximity to the hereinafter described roasting chamber floor to form a material admission throat or passage 28.

The rearwardly directed transverse edge of the wall portion 12b is spaced from the transverse top of the wall 20 to provide the material inlet 30.

The numeral 31 generally designates a hopper or material feed bin which has a bottom inclined wall 32, here shown as resting upon the top of the wall 20 and spaced at its forward edge from the lower edge 33 of the hopper feed wall to provide a material outlet which is aligned with and discharges into the inlet 30 for the passage of material therefrom into the roasting chamber through the throat 28.

The lower end of the bottom wall 14 is provided with the downwardly directed material discharge passage 34. This passage extends across the full width of the chamber C and rising from the bottom wall 14 on the rearward side of the outlet passage 34 is a transversely extending barrier wall 35, the forward face of which is spaced from the rearward face 36 of the wall 18 and the spaced oppos ing faces of these walls are downwardly divergent as shown so as to facilitate the smooth passage of material from the roasting chamber.

:It will also be seen that the fact 36 of the wall 18 rises a substantial distance above the top of the barrier wall 35 before reaching the lower part of the exhaust conduit 24 and accordingly forms a back stop against which the roasted material moves from the about to be described roasting floor. i

Rising from the bottom wall 14 between the barrier wall 35 and the upper rearward wall 20' are a number of short transversely extending roasting floor supporting piers. Certain of these piers which are designated 37, extend inwardly from the side walls 16 a short distance as shown in FIG. 2, the piers 37 at one side wall being aligned with those at the opposite side wall and the piers attached to each side wall being spaced apart lengthwise of the oven structure. Other short transversely extending piers designated 33 are disposed in the longitudinal center of the bottom wall, being in spaced parallel relation lengthwise of the wall M and terminating at their ends short of the side walls and these central piers 38 are disposed in line with the spaces between the side piers 37. The tops of the piers 37 and 38 and the tops of the walls 20 and 35 are in a common plane parallel with the wall 14 and have resting thereon the roasting chamber floor which is generally designated 39 to form the plenum chamber 40 which is supplied with air under pressure from a suitable source such as an air pump 41 through a Conduit 42, here shown as opening into the plenun chamber 40 through the bottom wall 14 and between a pair of the centrally located piers 38.

The floor 39 is preferably formed of a high quality castable refractory. However, it may be formed of sil con carbide if desired, as this material has a high resistance to abrasion and also has the desired strength for spanning the piers 37 and 33.

Where temperature limits permit, use may be made of cast iron for the floor structure. The castable refractory material is, however, preferred because of its resistance to relatively high temperature and for economical reasons.

The floor 39 is provided with a plurality of Slots 43 or other openings through which air may pass into the combustion or roasting chamber C. The floor may be formed in a single casting or as a single slab through which the air passing openings or slots 43 are formed by suitable means simultaneously with the casting or the floor may be constructed of preformed sections placed in position relative to one another and suitably spaced to provide the air passing openings or Slots.

Disposed below the lower end of the oven structure and in line with the outlet 34 is a transition unit which is generally designated 44. This unit conveys the material resulting from the roasting operation, from the outlet 34 downwardly onto a receiving table 45, which is located below and spaced from the open lower end of the unit 44. This table 45 is preferably formed as a hollow structure as shown with means, as indicated at 45', at opposite ends of the table, for connecting suitable water pipes or hoses for the table to circulate cool ng water through the table to prevent warping or distortion of the table by the hot material which may be dumped thereon from the unit 44.

The unit 44 may be designed as a hollow wall structure providing a water chamber into which cooling water may be introduced at the bottom part through a ppe 46 and removed from a pipe 47 at the top part of the strucure, in those conditions of operation of the oven where it may be desirable to reduce the temperature of the material leaving the oven, before it is discharged onto the table 45. The numeral 48 designates a conveyor which is located beneath the table 45 and onto which the material from the table 45 is caused to flow by an oscillatng distributor which is generally designated 49 and which comprises a tubular rock shaft 50 located in the vertical central plane of the open lower end of the unit 44- and the shaft carries a number of radially directed fingers ^1 which are rocked back and forth from a vertical pos tion, by rocking the shaft 50 in a suitable manner. This rocking action of the distributor 50 causes the material with which the unit 44 is filled to be forced outwardly to the lateral sides of the table 45 and then off of the table onto the conveyor as will be obvious. Where the material being fed onto the table 45 may be heated the tubular shaft 50 may be supplied with cooling water through a hose connection 52 to prevent damage to the shaft and the ngers 51. The hose connection may be made by a suitable swivel coupling 52' whereby the de sired rocking action may be applied to the shatt 50 by a suitable lever or crank 50' connected with any appropriate mechanism for imparting a back and forth movement of the lever.

As shown in FIG. 1, the transition unit 44- has the hollow side walls downwardly diverging with the inner faces of the walls in the planes of the inner faces of the walls 18 and 35 so that material will flow freely through the unit without packing.

In the operation of the oven structure for calcning limestone, for example, the properly sized limestone would be mixed with coal or coke in the correct porti on to supply the heat required for calcining. This mixture, here designated L, is placed in the bin or hopper 31 and the discharge mechanism embodied in the structure 49 is started.

The oven is preheated in a suitable manner before the mixture is allowed to pass into the chanber C from the hopper. One means -by which this preheating may be effected is by the use of suitable heating torches and to facilitate such use the side walls 16 of the structure may be provided with access openings 16a provided with suitable refractory doors lieb mounted as shown on the outer side of the wall 16. After the oven structure has been raised to the proper temperature the mixture is' allowed to pass into the chamber and air is forced into the chamber C from the plenum chamber 40 below the sloping -oor 39 and the coal or coke mixed with the limestone will be ignited and will 'be burned out by the time the solids reach the end of the sloping floor 39 down which the same moves by gravity.

The exhaust gases are permitted to escape or are withdrawn through the stack 226 at the lower end of the furnace or oven structure.

An example of the operation of the oven or furnace structure for reducing metallic oxide ores is as follows. The 'beneficiated finely ground ore is thoroughly mixed with the correct proportion of ground char and a suitable binder such as bentonite clay. This mixture is then pelletized and the pellets are dred. The dried pellets are fed into the preheated oven or roasting chamber C in the same manner as above described in connection with the limestone calcining operation.

The air supplied through the slots 43 in the sloping floor burns a part of the char to supply heat for the reduction and the balance of the char acts as the reducing agent for the metallic oxide. The reduced metal is withdrawn by means of the discharging mechanism 49 at the lower end of the unit 44.

As will be apparent from the foregoing the use of the cooler unit 44 is optional, being dependent on the ultimate use of the reduced metal.

Many westem phosphate ores have relatively large amounts of carbonaceous materials, as hereinbefore stated, which lower the :1 0 content and interfere with electric furnace operation. When these ores are fed through this preheated oven the air supplied through the slots 43 will burn off :the carbonaceous materials in the ore and thereby the percentage of 0 will be raised in the product, making it suitable for electric furnace feed.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is dened in the appended claims, and all. changes that fall within the mete s and bounds of the claims, or that form their -functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

I claim:

1. A calcining and ore reducing furnace, comprising an elongate structure having vertically spaced parallel top and bottom walls disposed at an inclination from the horizontal Whereby the structure has an upper end and a lower end, an upper rear Wall, a lower forward wall &084322 and upwardly converging side wails, an inclined apertured floor disposed between the top and bottom walls in Parallel relation with the top wall and dividing the space between the top and bottom walls into an upper combustion and roasting charnber and a lower plenum chamber, a transverse barrier wall rising from said bottom wall adjacert to said lower forward wall and connecting said walls, said floor being joined to said side walls, the upper rear wall and the barrier wall to form said plenum chamber, said barrier wall being spaced from said forward lower wall and forming a material outlet opening directed downwardly through the bottom wall, the said lower forward Wall having a rearwardly -directed'face rising above the adjacent barrier wall and forming a back stop for material moving off of the floor into said outlet opening, said forward wall having a products of combustion opening means thereabove leading into an exhaust stack, upstanding pie's disposed in the plenum chamber in *staggered relation on and eX- tending across said bottom wall and supporting said floor, means at the upper end of the structure for supplying a mixture of ore and combustible material to the combustion and roasting chamber, a material inlet means between said supply means and the combustion and roasting chamber by which a mixture of ore and combustible material is delivered -downwardly and in a forward direction onto said floor, means for eflecting concentration at said inlet means of heat from such mixture burning on said floor, and means for supplying combustion supporting air under pressure into said plenum chamber for passage through the apertured floor, the said staggered piers effecting relatively even distributi on of the air through the apertured floor for ensuring complete Consumption of the combustible material of said mixture.

2. The invention according t-o claim 1, wherein said means for effecting concentration of heat at said inlet 'means comprises a portion of said top wall formed to have an inner surface -disposed at a sharp downward and rearward inclination towards the inlet means and joning a short rearwardly extending surface portion lying in relatively closely spaced rearwardly converg-ent relationship with the floor and forming said material inlet means as a forwardiy expanding threat in which the mixture is su bjecte-d to concentrated heat which is directed downwardly theretoward by said inclined wall surface.

3. The invention according t o claim 1, Wheren said side walls have a series of door covered access openings through which to introduce heating means for preliminarly raisng the temperature of the combustion chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,527,309 Kel sey Oct. 24, 1950 2,531,975 Essex et al. Nov. 28, 1950 2,536,365 Har dwerk et al. Jan. 2, 1951 2,540,806 Berger Feb. 6, 1951 2,761,668 Sylvest Sept. 4, 1956 FOREIGN PATENTS 1,198,415 France Dec. 7, 1959 1,221,397 France June 1, 1960 

1. A CALCINING AND ORE REDUCING FURNACE, COMPRISING AN ELONGATE STRUCTURE HAVING VERTICALLY SPACED PARALLEL TOP AND BOTTOM WALLS DISPOSED AT AN INCLINATION FROM THE HORIZONTAL WHEREBY THE STRUCTURE HAS AN UPPER END AND A LOWER END, AN UPPER REAR WALL, A LOWER FORWARD WALL AND UPWARDLY CONVERGING SIDE WALLS, AN INCLINED APERTURED FLOOR DISPOSED BETWEEN THE TOP AND BOTTOM WALLS IN PARALLEL RELATION WITH THE TOP WALL AND DIVIDING THE SPACE BETWEEN THE TOP AND BOTTOM WALLS INTO AN UPPER COMBUSTION AND ROASTING CHAMBER AND A LOWER PLENUM CHAMBER, A TRANSVERSE BARRIER WALL RISING FROM SAID BOTTOM WALL ADJACENT TO SAID LOWER FORWARD WALL AND CONNECTING SAID WALLS, SAID FLOOR BEING JOINED TO SAID SIDE WALLS, THE UPPER REAR WALL AND THE BARRIER WALL TO FORM SAID PLENUM CHAMBER, SAID BARRIER WALL BEING SPACED FROM SAID FORWARD LOWER WALL AND FORMING A MATERIAL OUTLET OPENING DIRECTED DOWNWARDLY THROUGH THE BOTTOM WALL, THE SAID LOWER FORWARD WALL HAVING A REARWARDLY DIRECTED FACE RISING ABOVE THE ADJACENT BARRIER WALL AND FORMING A BACK STOP FOR MATERIAL MOVING OFF OF THE FLOOR INTO SAID OUTLET OPENING, SAID FORWARD WALL HAVING A 